This invention relates to a hydraulic pressure control device for a vehicle in which a proportional pressure control valve having a built-in spool valve is actuated by the force applied to the brake pedal to adjust (or amplify) the hydraulic pressure for the wheel brakes to a proper pressure, and more specifically a hydraulic pressure control device in which even if a pressure source including a power-driven pump fails so that the supply of hydraulic pressure therefrom has stopped, the brakes can be applied, and a brake device which uses it to improve travel safety.
A so-called brake-by-wire type vehicle brake device has been developed in which in order to electrically control the braking force applied to the vehicle, the hydraulic pressure generated by the brake operation by the driver is converted to an electric signal and the hydraulic pressure generated in the power line (that is, pressure source including a power-driven pump) is adjusted to a value corresponding to the electric signal before supplied to the wheel brakes.
Also, a proportional pressure control valve suitable for use with such a brake-by-wire type brake device has been developed and actually used.
FIG. 10 shows an example. In this proportional pressure control valve 60, a spool valve 62 is inserted in a housing 61 having an input port 61a, an output port 61b and a discharge port 61c to selectively connect the output port 61b to the input port 61a or the discharge port 61c by driving the spool valve 62 with a magnetic force generated by activating a coil 63a of a solenoid 63 and to adjust the degree of opening of passages defined between a shoulder portion on the outer periphery of the spool valve 62 and the edge of each port.
The input port 61a is connected to a pressure source 67 having a power-driven pump P and a pressure accumulator Acc. Also, the output port 61b is connected to wheel brakes 68 and the discharge port 61c is connected to a reservoir 69. By changing over the connection of these ports by the spool valve 62, the wheel brake pressure is increased and decreased, and in some cases, the output port 61b is separated from both the input port 61a and discharge port 61c to hold the wheel brake pressure.
The spool valve 62 has a difference in area between its pressure-bearing surfaces opposite to each other, the difference being equal to the sectional area of a pin 65 inserted in a pin hole 64. Thus, assuming that the hydraulic pressure introduced through the input port 61a is P, the force of a return spring 66 is F, the current supplied to the coil 63a is I, and the sectional area of the pin 65 is S, the thrust force acting against the spool valve 62 balances at a position where the following formula is met:
Pxc2x7S+F=axc2x7I2 (a is a constant) 
and the spool valve 62 stops at such a position.
The above formula is replaced with
P=(axc2x7I2xe2x88x92F)/S 
In this formula, a and S are constants. If the spring constant is ignored, F can also be regarded as a constant. Thus, the hydraulic pressure P is proportional to the square of the current I and corresponds to an electric signal controlling the current I, i.e. the brake operating amount that generates the signal.
The present inventors considered actuating the above-described proportional pressure control valve with a brake pedal.
A device in which the operating force of the brake pedal is used to drive the spool is disclosed e.g. in Japanese patent publication 2000-326839. In the device, only in an emergency (when electric line fails), the spool is adapted to be driven by the brake pedal, while in a normal state the spool is driven electrically. Thus, electronic control is indispensable, so that the device is complicated.
In contrast, in the device the present inventors have conceived, the brake pedal is coupled to the spool valve so that not only in an emergency but in a normal state, the spool is driven by the operating force to the brake pedal. Thus, in case braking force control is not necessary such as during regenerative blending braking, a braking force corresponding to the brake operating amount can be generated without electronic control.
With the device the present inventors are considering or the device disclosed in Japanese patent publication 2000-326839, the supply of hydraulic pressure to the wheel brakes is made only from the pressure source having a power-driven pump. Thus, while the pressure source is normal, even if the electric line should fail, it is possible to apply the brakes by driving the spool valve with the brake pedal. But if the pressure source fails and the supply of hydraulic pressure therefrom stops, the brakes would not work.
An object of this invention is to increase travel safety of the vehicle by eliminating such a trouble.
According to this invention, there is provided a hydraulic pressure control device comprising a housing formed with an input port, an output port and a discharge port, and a proportional pressure control valve and a hydraulic pressure generator mounted in the housing, the proportional pressure control valve having a spool valve and a return spring for biassing the spool valve, the spool valve bringing the output port into communication with the discharge port in a non-operated state, bearing hydraulic pressure on its opposed pressure-bearing surfaces having a difference in area, and moving to a balance point where the sum of the hydraulic pressure and the force of the return spring balances with an external force applied opposite thereto to change over connections of the output port to the input port and the discharge port, adjust the degree of opening of fluid passages, and adjust the hydraulic pressure at the output port to a value corresponding to the external force, the hydraulic pressure generator combined with the proportional pressure control valve, the hydraulic pressure generator comprising a second piston for transmitting a force to the spool valve through a second spring, a first piston for transmitting a force to the second piston through a first spring and an output port, wherein the first piston receives the brake pedal force as the external force, pressurizes and outputs brake fluid introduced into a fluid chamber between the first piston and the second piston.
Also, there is provided a brake device for a vehicle comprising the hydraulic pressure control device mentioned above, a pressure source connected to the input port of the hydraulic pressure control device, wheel brakes in a first line connected with said output port, wheel brakes in a second line connected with the output port of the hydraulic pressure generator, and a copy valve actuated by the hydraulic pressure difference between the first line and the second line to open and close a passage extending from the hydraulic pressure generator to the wheel brakes in the second line, the copy valve having a piston bearing fluid pressure in the first line on one side for pressurizing the wheel brakes in the second line, and a reservoir connected to the discharge port of the proportional pressure control valve, wherein brake fluid is supplied from the reservoir to a fluid chamber between the first and second pistons of the hydraulic pressure generator, and during failure of the pressure source, the hydraulic pressure generated in the hydraulic pressure generator is supplied to the wheel brakes in the second line.
The hydraulic pressure generator may be one in which the spring force of its first spring is greater than the sum of the force of the second spring and its sliding resistance or one in which a reactive force spring for returning the brake pedal is disposed between the second piston and the proportional pressure control valve. With the former hydraulic pressure generator, it is possible to lighten the force applied to the brake pedal during failure of the power source by providing a pressure-bearing unit having a piston for bearing the hydraulic pressure of the pressure source on one side and supporting one end of the reaction-force spring on the other side of the piston of the pressure-bearing unit. Also, with the latter hydraulic pressure generator, it is possible to generate hydraulic pressure immediately after depressing of the brake pedal during failure of the pressure source or the first line. Further, the reaction-force spring can be mounted in the hydraulic pressure control device.
The hydraulic pressure control device of this invention includes a hydraulic pressure generator that pressurizes brake fluid with the operating force to the brake pedal and outputs it. The brake device using it can pressurize the wheel brakes in the second line with the hydraulic pressure generated in the hydraulic pressure generator if the pressure source or the first line fails. Also, during failure of the second line, it is possible to pressurize the wheel brakes in the first line with the hydraulic pressure adjusted by the proportional pressure control valve. Thus, even if a failure occurs anywhere, at least one line will positively survive, so that reliability improves.
Preferred embodiments and their functions and effects will be detailed below.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: